Refuse collection trucks commonly include a tailgate device for receiving refuse and for forcing the refuse forwardly into the container of the truck. An example of such a refuse collection truck is illustrated in the Weischel et al. U.S. Pat. No. 3,682,336, issued Aug. 8, 1972. One problem with prior art refuse collection trucks is that material being forced into the truck container is not uniformly compacted. The material at the forward end of the truck is commonly not as tightly compressed as the material at the rearward end of the truck. This reduces the load which can be carried by the truck and reduces the efficiency of operation of the truck.
The Urban U.S. Pat. No. 3,049,256 teaches a refuse compaction structure intended to overcome the problem of variation in the amount of compaction of refuse in a refuse container. The refuse collection truck shown in this patent is provided with a movable ejection plate or panel housed in the refuse container and supported for movement along the length of the container. During initial loading of the truck, the ejection panel is positioned at a rearward portion of the truck, and the refuse material can be compacted against the ejection panel by the packing plate of the tailgate. The ejection panel is supported by a telescoping ejection cylinder, and a relief valve is connected to the telescoping ejection cylinder such that the ejection plate can move forwardly as the pressure exerted by the refuse material on the ejection panel and as the internal pressure in the ejection cylinder exceeds a predetermined pressure.
One of the problems with this prior art arrangement lies in the use of a telescopic cylinder to control the ejection panel. When the first refuse material loads are compacted in the unit, the ejection panel is at the rear of the truck body with the telescopic cylinder fully extended. The force on the rear face of the ejection panel necessary to cause the predetermined pressure in the ejector cylinder for release will be this predetermined pressure multiplied by the cross-sectional area of the smallest stage of the telescopic cylinder. As the truck body fills and the ejection panel moves forwardly in the body, the larger stages of the telescopic cylinder come into use. Due to the larger cross-sectional area of these telescopic cylinder stages, the force necessary to cause the panel to release is larger. As a result, as the truck body is filled, greater force must be applied to the ejection panel to cause it to release. Due to this condition, it is not possible to provide for the application of maximum compaction forces for the early stages of compaction because as the body becomes filled, there would be insufficient force available to move the larger stages of the telescopic ejection cylinder. As a result, smaller initial compaction forces must be used with attendant loss of compaction efficiency.
Attention is also directed to the McCarthy U.S. Pat. No. 3,556,324 showing another refuse packing system and a pilot operated unloading valve arrangement for controlling the forward movement of the ejection panel. The pilot operated unloading valve arrangement included in the McCarthy structure seeks to cure the deficiencies of the structure shown in the Urban patent. The McCarthy arrangement connects a pilot operated unloading valve to the packing side of the packing cylinder such that when the pressure in this side of the packing cylinder reaches a predetermined packing pressure, the pilot operated unloading valve relieves the ejector cylinder, thereby allowing the ejector panel to move forwardly. With this arrangement, the only time the ejector cylinder can relieve is when the pressure in the packing side of the packing cylinder exceeds the setting of the pilot operated unloading valve. This arrangement does not provide for interruption of the exhaust of the hydraulic fluid from the ejector cylinder when the packing control valve has been moved to a neutral position and there is a high fluid pressure in the packing cylinder due to the compressed refuse material maintaining back pressure on the packing cylinder. In the event this back pressure exceeds the pilot operated unloading valve setting, the ejector panel can unload after the packing cycle has ceased, thus reducing compaction efficiency.
In another embodiment of the structure shown in McCarthy, the pilot operated unloading valve is connected to the pump pressure line rather than to the packing cylinder. This arrangement functions in the same manner as the first embodiment, provided that the highest circuit pressure in the pump pressure line is generated by the packing pressure. The hydraulic circuit design has to be such that this is the case or premature unloading of the ejection panel could occur. In addition, the use of mechanical controls, the existence of transient pressure peaks or spikes, and pressure drop in the hydraulic lines between the pump and the tailgate can allow the ejection cylinder to unload prematurely, thereby permitting the ejection panel to move forwardly before the area behind the ejection panel has been completely filled with compacted refuse material.